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Hendra Virus Hits Australia's Horse Population

Deadly virus spread by fruit bats

The latest outbreak of Hendra virus has rocked Australia's equestrian industries. The first outbreak of the virus occurred in 1994 and threatened the running of the Melbourne Cup, Australia's premier horse-race. The nation comes to a standstill on Melbourne Cup day which is the first Tuesday in November. It was almost unthinkable that anything could cause its cancellation. But with a trainer and fourteen horses dead, it was obvious that something serious was afoot.

This deadly new Hendra virus was affecting horses and humans alike and looked like putting a stop to the movement of horses throughout the country. The equestrian industry was thrown into disarray largely because the disease had never been encountered before.

The Hendra virus is now known to be related to the Nipah virus which has caused many deaths in the populations of Malaysia, Singapore, Bangladesh and neighbouring countries.

The Hendra virus continues to cause problems in the equestrian industry. In the last seventeen years, seven cases have been recorded of humans catching the disease. Four of these resulted in death. Two of those who died were Queensland veterinarians.

Hendra virus has struck again recently, with confirmation of deaths from the virus as recent as July 22, 2011. Eight incidents are currently being managed in Queensland. There has been a death in Chinchilla which is the first confirmed case west of the Great Dividing Range. Two unrelated incidents were confirmed on 16 July and one on 12 July. The 12 July case was on a property west of Cairns where 36 horses are now being tested.

The virus is transmitted by fruit bats (flying-foxes) which are believed to be the natural hosts. The virus has little effect on the bats but once transmitted to horses and through horses to humans, the disease is lethal. Flying foxes which carry the virus excrete live virus in their faeces, urine and saliva for about a week although they show no other signs of illness. It is thought that the virus is ingested by horses eating feed that has been contaminated by bat secretions.

The virus first struck in September 1994 when a Queensland horse trainer Mr Vic Rail fell ill as did a stable hand and most of his horses. Within a few days, Rail and 14 horses had succumbed to what was then a mystery illness. The Australian Animal Health Laboratory (AAHL) in Geelong, Victoria, a division of the CSIRO, isolated and identified a virus which at that time was unknown anywhere in the world.

As at July 2011, there have been 23 occurrences of Hendra virus. All have been on the east coast of Australia between Cairns, Queensland in the north and south to Macksville in northern New South Wales. All sites have populations of at least two of the four mainland flying fox (fruit bat) species. The pattern of the outbreaks has been seasonal suggesting that infection coincides with the times when the little red flying-fox, grey-headed flying-fox, black flying-fox and spectacled flying-fox give birth. Infection of humans is believed to be only through an intermediate host, in this case the horse.

In equines, there is usually pulmonary oedema and congestion, together with neurological signs. In humans, symptoms may be related to haemorrhage and oedema of the lungs or to encephalitic symptoms, resulting in meningitis.

The Hendra virus is a paramyxovirus and related to the Nipah virus. Sungai Nipah is a village in Malaysia which was affected by an outbreak of disease in 1998-99. The Hendra and Nipah viruses form a new genus (Henipavirus) of the paramyxovirus family.

The Hendra disease is named after the suburb of Brisbane where the first outbreak occurred. Once the cause of the disease was established, AAHL researchers were able to develop diagnostic tests.

There is no evidence of the disease spreading from human to human, human to horse or bat to human. Hendra virus is a notifiable disease in Australia and all suspected cases must be reported to the relevant authorities. Although outbreaks have been confined to Queensland and northern New South Wales, the potential exists wherever there are populations of fruit bats.

Horses exhibit a range of clinical signs including rapid onset, increased temperature, fever, increased heart rate, discomfort and weight shifting, depression and early death associated with respiratory or neurological signs.

Respiratory signs include distress, increased rate of respiration and nasal discharge. The discharge may be clear at onset, developing to white froth and/or blood-stained froth.

Neurological signs are aimless walking, restlessness, head tilting, unsteady gait, circling, some apparent loss of vision, twitching of muscles, incontinence of urine and an inability to rise.

There have been a range of observations reported in individual horses affected with the virus. If you think your horse may have the virus, contact the authorities, shower and shampoo your hair, change your clothes (including footwear) and stay away from other horses. If you must tend to the sick horse or others, wear protective clothing. Wash your hands thoroughly after handling any horse.

Because horses can be infected before showing signs of illness, high standards of hygiene should be maintained in all dealings with horses. Thorough washing of hands, careful attention to treating and covering wounds or cuts and avoiding unnecessary close contact such as kissing horses on the muzzle are all practices that need to become standard in areas subject to Hendra virus.

To avoid contamination, place food and water containers under cover but not under trees. This will help avoid contamination from bat droppings or secretions. Do not give foods that will attract bats such as apples and carrots. Don't use molasses or sweet foods. If possible, remove horses from paddocks around dusk and through the night when bats are most active. Maybe fence off treed areas which are frequented by the bats. Keep any horses that appear off-colour isolated until seen by a vet and given the all clear.

If Hendra virus is suspected, isolation of the sick animal is vital. Disinfect or clean any gear which has been exposed to body fluids before using it on another horse eg twitches, halters. Ask your vet which disinfectants are most appropriate. Don't bring sick horses on to your property and obviously don't take sick horses off the property.

Humans affected with Hendra virus exhibit influenza-like symptoms. These include as fever, sore throat, cough, headache and weariness. Inflammation of the brain (encephalitis) causes headache, high fever and drowsiness. This can lead to convulsions and/or coma and death. The incubation period (time between exposure to a sick horse to onset of illness) has varied from 5 to 21 days.

The mortality rate in horses is over 70% so this is not a disease to be ignored. Once notification of a suspected outbreak is received Biosecurity Queensland has in place a range of management strategies. The property is immediately placed under quarantine and sick animals are isolated. A full investigation is carried out and measures taken to protect the public, care for the animals, decontaminate the area and safely dispose of dead animals.

It is very difficult to avoid outbreaks of the disease. It is not feasible to cull the flying foxes. They are protected native fauna and are a natural part of the ecosystem, playing an important role in pollination and seed dispersal in native forests. They are a highly mobile species and, should an area be cleared of them, others will move in.

The infection is picked up by coming in contact with the bodily fluids of sick horses, both before and after clinical signs are evident, and during autopsies. Respiratory and nasal secretions, saliva, urine and tissues are especially to be avoided. When handling cases, full protective clothing should be worn including impervious overalls, gloves, boots, respirator mask and face shield.

Hendra virus is alive and well but there are now a few more strategies in place to restrict its impact and spread.